In a diesel engine, high pressure fuel injection is required in order to improve engine performance and fuel economy and to reduce exhaust emissions. In recent common rail systems, the maximum pressure of injected fuel is about 1800 to 2000 bar. In such systems, high pressure fuel that is pressurized by a high pressure fuel pump is supplied to a common rail through a fuel pipe, and fuel in the common rail is injected through a fuel injector according to control of an engine control unit (ECU).
In general, fuel pumped by a fuel pump is supplied to a common railt through a fuel feed line. Fuel is supplied to each fuel injector from the common rail and the fuel is then injected into combustion chambers at a high pressure. The fuel injector typically includes a solenoid, an anchor bolt, an anchor plate, a ball, a nozzle spring, a valve spring, a valve piston, a needle, or the like. The needle undergoes vertical movement according to operation of the solenoid, and the fuel injector injects fuel according to the vertical movements of the needle. Therefore, through control of the solenoid, fuel injection timing, an amount of injected fuel, and injection times, the fuel injection can be controlled.
However, because a high fuel pressure is maintained in such a common rail system, fuel is suddenly injected even in an early stage of engine starting. Therefore, an ignition delay may occur and knocking noise increases, and temperature in the combustion chamber may substantially increase so that exhaust gas (e.g., NOx) is increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.